No audio available for this content. Hantaviruses are a group of viruses carried by rodents, the World Health Organization (WHO) says. It can cause severe disease in humans, who often become infected via contact with infected rodent urine, droppings, or saliva. In the case of the outbreak on the Oceanwide Expeditions cruise ship, MV Hondius, a married couple is believed to have contracted the virus when they disembarked to explore an island teaming with wildlife.